Solve Gas Law: Volume at STP from Pressure & Temp of Hydrogen Gas

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SUMMARY

The discussion focuses on calculating the volume of hydrogen gas at Standard Temperature and Pressure (STP) given its initial conditions: 745 mm Hg and 25°C, with a vapor pressure of water at 23.8 mm Hg. The correct approach involves using the ideal gas law (PV=nRT) and adjusting for the vapor pressure of water to find the pressure of dry hydrogen gas. The final volume at STP is determined by converting the initial conditions to STP using the corrected pressure of the hydrogen gas.

PREREQUISITES
  • Understanding of the Ideal Gas Law (PV=nRT)
  • Knowledge of Standard Temperature and Pressure (STP) conditions
  • Familiarity with vapor pressure concepts
  • Ability to perform unit conversions (mm Hg to atm)
NEXT STEPS
  • Learn how to apply the Ideal Gas Law to different gas conditions
  • Study the concept of vapor pressure and its impact on gas calculations
  • Explore methods for converting pressure units (e.g., mm Hg to atm)
  • Investigate real-world applications of gas laws in laboratory settings
USEFUL FOR

Chemistry students, educators, and anyone involved in gas law calculations or laboratory experiments involving gases will benefit from this discussion.

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Homework Statement


Hydrogen gas is collected over water at 25°C. The atmospheric pressure in the room is 745 mm Hg and the volume of gas in the container is 43.5mL. The vapor pressure of water at 25°C is 23.8 mm Hg. Determine the volume the gas would occupy at STP.


Homework Equations


PV=nRT
PV/NT=PV/NT
standard pressure=760 mm Hg or 1 atm
standard temperature= 273 Kelvin


The Attempt at a Solution


Well for this one I wasn't really sure if they just gave me excess information to throw me off. My first response was to say that the volume would just be 43.5mL. None of the equations provided above worked with just the information given. Is this really as easy at it seems?
 
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No, it is not that easy, and there is no excess information.

First of all, you know the volume at 745 mmHg and 25°C, these are not STP conditions, so the answer can't be 43.5mL.

Then, some of the volume is taken by the water vapor, and you are asked about the volume of just hydrogen - so you have to take 23.8 mmHg into account. What is the pressure of the dry hydrogen in the collected sample?
 

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